Using the word 'Myself'

'Myself' is a word, which a lot of people tend to use incorrectly.
The rule is, that it is incorrect to use myself in a sentence that does not have an 'I'.

E. g.

I did this myself. (correct)

The word myself is a pronoun, it can either be an emphatic pronoun or a reflexive pronoun.

I did this myself - here 'myself' is an emphatic pronoun because there is an emphasis on how you did something. Similarly, I pricked myself with a pin - here 'myself' is a reflexive pronoun. When 'myself' is used to show that you are doing something to yourself it is reflexive.
'Myself' cannot be used for any other reason. It cannot be interchanged with I or me. It cannot be used when someone is doing something to you.

E. g.

He raised an issue with myself. (incorrect)

He raised an issue with me. (correct)

While giving an introduction:
Many people tend to introduce themselves as: "Myself Rohit" (this is incorrect). The correct way to introduce would be: "I am Rohit".

Also, John and myself went for a walk (incorrect).

John and I went for a walk. (correct)

'Myself' cannot be used without an 'I' in the same sentence and for the same reason saying "myself stepped on the puddle" would be incorrect. "I stepped on the puddle" will be correct.